As I said before in an older post, there is no right or wrong when it comes to define what is correct for Street Photography in regards of focal length. You can either choose to snipe your subject from afar to have a more distant and colder approach, or you can get in the middle of the action with a shorter focal length. All in all, we still have to be respectful in either case. We can't be stalking strangers like lunatics, whether this is done by afar or at close range not only because this is going to bring a whole lot of attention towards us (not to mention an increased risk to our physical integrity), but as well because the Street is not a place where we can observe people like if they were in a Zoo without showing a little bit of respect.
Yes, Street Photography is a wonderful tool to analyze society in a given place at a given time; a sample taken that some day could be used for some historical value, but still as human beings we have to show respect for other human beings. In my humble opinion, running through a street while photographing and flashing unexpected people is just completely disrespectful. There are a couple of examples out there (and some of them even have their own internationally acclaimed workshops) that consider themselves street photographers... and I wonder how do they got recognition. I do accept that their "style" is daring, but it fails to show any respect for the subject. At all. (Talking about daring, I dare them to do the same in the Gulf countries. They would last no more than few mins before they get the attention of the local authorities).
Other thing that I find lacking any type of respect is photographing beggars and vagabonds. I'm not talking about doing it as for an assignment or a project, but just doing it stealthy and candidly for no reason whatsoever. I have seen several people photographing the beggars in Prague (sadly, they are kind of famous by the way they beg for money, you can google more information about it) and I wonder what is the force that drive them to do so: do they think they will help by doing that? Are they taking images so they can show them to their friends back home? Because if that's the case, you don't need to do so, you can refer them to google. Do they think that an image of a poor fellow in the street asking for money in black and white with a gorgeous light will become art? That's just plain sick. Period.
The fact that we hold a camera (and sometimes, we have technical knowledge) does not give us the right to do as we please and photograph indiscriminately around the streets like we own them. Take images, document, but always show respect. You ask for a portrait and you got a "no" for an answer? Say thank you and walk away. You wanted to take a candid and you got spotted? Smile and wave your hand. They asked you to delete the picture from your memory card? Do so, apologize and walk away. You wanted to get a shot of a certain subject in a certain way and you could not? Do not follow and stalk people like a psychotic maniac... try to visualize yourself from outside: do you like how it looks? Ok, your subject does not either.